Monsters Inside Me
Toxoplasmosis
Caused by Toxoplasma gondii, aka the "cat poop" parasite.
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The Parasite: Toxoplasmosis is caused by a protozoan parasite known as Toxoplasma gondii. Members of the cat family are the only known hosts for the sexual stages of this parasite, and they are therefore the primary reservoirs of infection. The parasite's life cycle begins when it breeds in the small intestine of an infected cat. It produces large numbers of oocysts or spores, which are excreted, and then often eaten by rodents such as rats or mice. Strangely, once infected these rodents undergo a neurochemical change. The parasite actually manipulates the part of the rodent's brain that triggers fear and avoidance of cats. With this change in neurochemistry, it is highly likely that the infected rodent will be caught and eaten by a cat, thus continuing the parasite's life cycle.
Humans may become infected with Toxoplasmosis by accidentally ingesting the parasite in oocyst form through food or other types of contamination. A cat's feces can contaminate household items (obviously, litter boxes are particularly prone to contamination), soil and even drinking water. Contact with contaminated items or substances can lead to infection. Pregnant mothers can also pass the infection along to their unborn child.
The Infection: Once the parasite has infected a human host, it forms tissue cysts, generally in skeletal muscle, the brain and eyes. Although many people contract Toxoplasmosis, most do not exhibit symptoms because their immune system keeps the parasite in check. When illness does occur, it is usually limited to mild flu-like symptoms. These symptoms last for several weeks and then disappear. However, the parasite can remain in the body in a dormant state and can become reactivated if the host's immune system is compromised. Acute eye disease, specifically retinochoroiditis, can be caused by Toxoplasmosis and can lead to loss of vision.
Research is also being done into the possibility that Toxoplasma gondii plays a role in altering human behavior and may be linked to neurological diseases like schizophrenia. In the case of congenital (mother-to-fetus) transmission, Toxoplasmosis can cause miscarriage, a stillborn child or a child born with signs of Toxoplasmosis, such as an abnormal enlargement of the head.
Treatment: Most healthy people will recover from Toxoplasmosis without treatment. A combination of drugs, including pyrimethamine, sulfadiazine and folinic acid can be used to treat individuals that develop more severe symptoms. Additional treatment is usually necessary for pregnant women, infants, people who develop eye disease and individuals with compromised immune systems.
Prevention: To reduce the risk of being infected with Toxoplasmosis through food, cook all food to safe temperatures to avoid eating contaminated meat. Freezing meat for several days before cooking can also reduce the risk. Peel and wash fruits and vegetables thoroughly. Drinking water should be avoided in less developed countries. When gardening, gloves should be worn and hands should be thoroughly washed after contact with sand or soil. Cats should be fed only canned or dried commercial food, never raw or undercooked meats. The litter box should be changed daily and hands should be washed with soap immediately afterward. Pregnant women should not change the litter, if possible. Cats should be kept indoors to avoid ingesting an infected rodent and humans should not adopt or handle stray kittens. In particular, new cats should not be adopted during pregnancy.
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Featured in Living With the Enemy, Episode 5 of MONSTERS INSIDE ME
Killers? No. Users? You betcha. These parasites keep the party going for as long as possible. Highlighting malaria, the pork tapeworm and Toxoplasmosis.
 Check out Toxoplasma gondii in action.
Visit the Monsters Inside Me video gallery.
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  Livin' La Vida Parasita! Find out how parasites affect our mind, our health and our lives in this series of articles from HowStuffWorks.com.
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 Rate Disgusting Parasite Habits: From blood-sucking to brain-eating, rate revolting parasite habits on a scale from "gross" (0) to "I think I'm going to vomit" (10).
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